Abstract: An enclosure structure for housing switchgear apparatus (such as circuit breakers) is fabricated from a pair of sheet metal panels that are held in precisely-spaced upstanding relationship by a plurality of metal cross-struts of U-shaped cross-section which mechanically interlock with apertured portions of the panels and are held in such position by triangular-shaped metal gussets which overlap and are bolted to adjacent portions of the cross-struts and panels. The cross-struts are provided with longitudinally protruding tangs at each end that are slip-fitted into and interlock with slot apertures in the panels. The width dimension of the finished enclosure structure is precisely controlled by positioning tabs on the ends of the cross-struts that are offset from the associated tangs and are drawn into abutting relationship with the inner surfaces of the respective panels when the structure is bolted together.